In an image forming apparatus such as an electrophotographic copier, a facsimile, and a printer, there is a sheet-conveying device, when supplying sheet such as sheet of paper and sheet-like films from a paper supply cassette device or a paper supply tray, for clamping the sheet by a separation sheet and a conveying roller or a separation roller and a conveying roller and supplying only the top of sheet. Further, there is a sheet-conveying device for clamping the sheet supplied and separated from the paper supply cassette device or paper supply tray by the conveying roller and a driven roller and conveying them in a predetermined direction. In such a sheet-conveying device, to stably convey sheet, in Japanese Patent Application 2002-356242, to pressurize a roller pair symmetrical left and right composed of a conveying roller and a driven roller, a constitution of pressuring the left and right shafts of the driven roller separately from each other using two springs is disclosed.
However, like the conventional device, when the driven roller is pressurized to the conveying roller using the left and right separate pressing means, the pressure of the driven roller to the conveying roller becomes imbalance due to variations in the left and right pressing means and the clamping and conveying force by the left and right conveying roller and driven roller pair becomes imbalance. Therefore, during conveyance, sheet is skewed, and conveying defects such as jamming and bending of front ends are caused, or the sheet must be greatly repositioned by an aligning roller. And when the repositioning by the aligning roller is not sufficient, a problem arises that the image quality is decreased due to image displacement. The same may be said with the conveying roller for separating and conveying only the top sheet.
Therefore, a sheet-conveying device and an image forming apparatus for causing no skewing when clamping and conveying sheet by the conveying roller and driven roller or the conveying roller and separating member, preventing conveying defects, repositioning surely the front ends of sheet at the position of the aligning roller, thereby obtaining good images are desired.